Various water-emulsifiable synthetic esters have been suggested as lubricants for fibers but they are not without certain disadvantages. Some of these synthetic esters are viscous liquids and require the use of additional emulsifying agents because otherwise they give relatively unstable emulsions, whereas certain others contain a plurality of free functional groups such as hydroxyl groups, and are thermally unstable. Heretofor it has not been possible to produce low viscosity synthetic lubricants showing a good combination of lubricating efficiency and emulsifiability in water and thermo-stability, i.e. resistance against degradation due to heating under lubricating conditions.